Fluctuation characteristics of geomagnetic field over Chinese mainland based on fixed geomagnetic observatories data

The fluctuation characteristics of the geomagnetic field are crucial for understanding the internal geophysical processes and monitoring changes and predicting future trends in the geomagnetic field. Given the complexity of geomagnetic field fluctuations, this study analyzed the fluctuation characteristics of the hourly mean time series from the geomagnetic D, H and Z components recorded by 68 fixed stations across Chinese mainland in 2023 using the multifractal detrended fluctuation analysis (MF-DFA). The results revealed that geomagnetic field fluctuations over Chinese mainland exhibited significant multifractal characteristics. The fluctuation function displayed three scale intervals, demonstrating multiscale properties and the invariance characteristics of scale interval segmentation. The spatial variations of the generalized Hurst index at small and medium time scales further validated the multiscale nature of geomagnetic field time series. The differences in long-term memory properties among different geomagnetic components at medium time scales may be attributed to their differential responses to various geomagnetic activities. The spatial similarity between the multiple fractal spectrum width and the generalized Hurst index at medium time scale suggested that persistence enhanced the multiscale inhomogeneity of temporal amplitude fluctuations. The fluctuation amplitude in the D and Z components was pronounced, while the fluctuations in the H component remained relatively uniform. Geomagnetic field fluctuations exhibited distinct spatial heterogeneity. The D component exhibited a longitudinal effect, while the H and Z components displayed pronounced latitudinal effects. This indicated that the dipole geomagnetic field exerted a dominant control over regional geomagnetic field fluctuations.